Field of the Invention
The invention relates to a method for producing a gasoline engine exhaust gas system having a particulate filter. The invention further relates to an exhaust gas system of a gasoline engine in the state before the first heating up of the exhaust gas system.
Description of the Related Art
Current legal requirements for reducing fuel consumption and simultaneously tightening the particulate limit values (mass and number) increasingly present a challenge for the development of internal combustion engines. The compliance with future particulate limit values in accordance with the required boundary conditions will impede future efforts of reducing consumption. This will lead to virtually all internal combustion engines in future having a particulate filter, as already is the case in diesel engines.
Soot from combustion is deposited in the particulate filter and converted again into gaseous constituents by a specific regeneration of the filter. Furthermore, ash constituents that originate in engine oil additives and/or fuel additives remain permanently in the filter. The soot loading of the filter currently is detected by a counterpressure measurement and redundantly via a calculation model. Active measures for soot regeneration are initiated depending on the soot level. However, the counterpressure measurement (Δp=f (soot loading)) has a pronounced hysteresis, and therefore a clear association between the loading of the particulate filter with soot and the counterpressure is not provided. Regeneration based on a calculation model generally is too early because of the strong fuel influence, in particular because the number/mass of particulates may vary by a factor of 5 between fuels. A reduction of the hysteresis of the counterpressure is desired to obtain a clear control variable for the regeneration of the particulate filter. At the same time, in a situation without hysteresis behavior, a more stable protection of the components can also be ensured since specifically highly loaded edge zones can be detected better by counterpressure measurement.
Current particulate filters have two filter functions, namely, depth filtration and surface filtration. Soot deposition thus leads in the first step to depth filtration with a high pressure rise and in the second step to surface filtrations with a smaller pressure rise.
Depth filtration deposits particulates in the wall of the particulate filter. Surface filtration takes place on the surface of the filter. Over an operating period, the particulate filter becomes ever more from the depth filter to the surface filter. Depth filtration is associated with a high pressure rise, since the permeability of the exhaust gas is influenced negatively. If the pores in the wall are substantially coated with soot, the soot subsequently primarily accumulates on the wall. This surface filtration leads to a moderate pressure rise, smaller than in depth filtration. If the soot in the filter then is regenerated, the pressure is dissipated with a hysteresis behavior characterized by a large pressure drop in a first step, and subsequently with a moderate pressure drop.
In contrast to soot, the ash in the particulate filter always accumulates on the wall and not in the wall. Soot cannot penetrate the ash layer, and thus the ash fundamentally and irreversibly prevents the depth filtration of the soot. The pressure rise with increasing soot deposition produces a linear relationship without hysteresis over the entire region. Thus, the quality of determining the soot loading by a counterpressure measurement is increased significantly so that soot regeneration strategies can be controlled in a more target-oriented and consumption-optimal manner.
To solve the above-described problem, an ash layer would have to be applied in the form of a filter cake to the surface of the duct walls of the particulate filter in the new state; consequently, it would have to be applied before the first heating up of the exhaust gas system.
WO 2014/183998 A1 discloses a method for determining soot loadings of a particulate filter in gasoline engines. The determination of the admitted soot loading comprises taking into consideration predetermined soot portions of soot-relevant events of a standardized driving cycle.
It is known, during the production of exhaust gas systems, to install plastics rings as spacers in the exhaust gas system. These rings function during the manufacturing process to ensure that the components are positioned correctly with respect to one another and maintain the required distance from one another. The spacer rings are no longer required after the parts are welded together. The plastic rings are burned during the first heating up of the exhaust gas system by the engine, and the components in the interior of the exhaust gas system have the necessary free movement that they require during operation.
It is an object of the invention to provide a method for producing a gasoline engine exhaust gas system having a particulate filter where the method applies an ash layer to the particulate filter in an extremely simple manner. In particular, an object of the invention is to provide a method for applying an ash layer as a filter cake to the surface of the duct walls of the particulate filter. A further object of the invention is to provide an exhaust gas system of a gasoline engine with a structurally extremely simple design that permits a targeted application of an ash layer.